The present disclosure relates generally to turbochargers having a variable-nozzle assembly made up of an array of circumferentially spaced vanes supported by a nozzle ring and rotatable about respective axes defined by vane shafts that extend through bearing apertures in the nozzle ring, wherein a unison ring engages vane arms that in turn are affixed to the vane shafts such that rotation of the unison ring in one direction or the other causes the vanes to be pivoted to vary their setting angles, whereby the effective flow area through the nozzle is varied.
Such a variable-nozzle assembly typically is actuated by an actuator (e.g., a diaphragm actuator) connected via a mechanical linkage to the unison ring. The variable-nozzle assembly must be calibrated to ensure that a given position of the mechanical linkage corresponds to the desired positions of the vanes, so that for example when the mechanical linkage is placed in a position that is supposed to produce a minimum flow rate through the nozzle, the vanes will truly be in the proper positions to provide a minimum effective flow area through the nozzle.
This calibration process typically is performed during the assembly of the turbocharger, by installing the variable-nozzle assembly in the turbocharger and then supplying air into the turbine housing so it flows through the variable-nozzle assembly. A pertinent parameter (e.g., turbocharger rotational speed) is monitored while the variable-nozzle assembly is actuated to vary the vane setting angles until the monitored parameter reaches a predetermined level (e.g., until the turbocharger speed reaches a minimum value such that rotating the vanes in either direction from the minimum-speed position causes the speed to increase). Once the desired vane position is attained, the mechanical linkage is adjusted if necessary so that a predetermined position of the linkage produces the desired result.
The need for calibration of the variable-nozzle assembly during the assembly of the turbocharger substantially complicates and slows down the assembly process.